Turbine blades in gas turbine engines are frequently provided with flange portions at their radially outer ends which cooperate with those of circumferentially adjacent blades to define a radially outer wall of the annular gas duct through which a major portion of the combustion products of the engine flow. These flange portions are normally referred to as forming the "shroud" of the blade, and where the term "shroud" is used in this specification it will have this meaning.
Gas turbine engine turbine blades are typically required to operate in an extremely high temperature environment, usually greater than the melting point of the alloy from which the turbine blade is manufactured. In order that the turbine blade is able to function effectively in this sort of environment, it is cooled by air tapped from the engine's compressor. The relatively cool air is directed into passages which extend from one end of each blade to the other. If the turbine blades in question are provided with shrouds, some of that cooling air may be directed into passages provided within the shrouds to cool them before being exhausted into the hot gas stream flowing over the turbine blades. Providing such cooling passages in the shrouds usually dictates the use of expensive machining techniques which inevitably result in high manufacturing costs. Additionally since there are limits to the size of the cooling passage which can be incorporated into a shroud, the shroud is frequently thicker than should otherwise be the case.